JPH058441A - Imaging device - Google Patents

Abstract

PURPOSE:To prevent the fogging of the surface of the lens array of an imaging device by protecting the surface from ozone generated by discharge in a copier, to also prevent the disturbance of an image by flattening the surfaces of lenses and to correct the irregularity of focus positions at every lenses. CONSTITUTION:A film of a transparent synthetic resin 4 is provided to the surface of a lens array not only to block a lens 2 from nitric acid mist generated from ozone but also to flatten the surface of the lens 2. The thickness of the transparent synthetic resin 4 to be applied is determined based on whether the lens 2 is a long or short focus and the transparent synthetic resin 4 is applied so as to become thick on the side of a light source surface 6 in the case of the long focus and on the side of an image forming surface 8 in the case of the short locus.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image device such as an LED printer head, a liquid crystal shutter printer head, and a contact image sensor, and more particularly to improvement of a lens array used.

[0002]

2. Description of the Related Art Printer heads in which an LED array or a liquid crystal shutter array and a lens array such as a self-focusing lens array are combined are well known. Further, a contact type image sensor in which a lens array such as a self-focusing lens array and a photoelectric element array are combined is also known. In these imagers, the performance of the lens array is important.

However, as the first problem of the lens array, there is variation in focus. The dispersion of the focal point of the lens array is caused by the dispersion of the refractive index distribution within the lens, the dispersion of the length of individual lenses, the deterioration of the lens alignment degree such as the deterioration of the pitch accuracy of the lens or the inclination of the lenses. .. A second problem of the lens array is that the lens surface is fogged by ozone or the like generated at the discharge portion of the photosensitive drum of a copying machine or the like. The clouding due to ozone progresses when ozone generated by corona discharge reacts with nitrogen to generate nitrogen oxides, and the generated nitrogen oxides react with moisture to become nitric acid and adhere to the lens surface.

The problem of focus variation of the lens array is particularly remarkable in a plastic lens, and in the case of a plastic lens, there is another problem that the lens surface is not flat. This is because the plastic lens array is obtained by simply bundling and cutting the plastic lenses, and the scratches at the time of cutting remain on the lens surface. The uneven surface of the lens array causes image distortion. The problem of fogging due to ozone is particularly remarkable in glass lenses. In the case of a glass lens, when nitric acid mist adheres to the surface, the alkaline component in the glass is deposited and the lens becomes cloudy. The cloudiness of the lens is not limited to ozone, and similarly progresses with nitrogen oxides and sulfur oxides generated by air pollution. Such fog can be wiped off with alcohol or the like, but it is difficult to clean the surface of the lens array of the image head incorporated in a copying machine, a printer / facsimile, or the like. With a conventional image head using a glass lens, 50
When it is used for about 0 hours, the output is reduced by about 10%, and the problem of lens fogging becomes a serious problem.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the occurrence of fogging of a lens array due to ozone or the like, and prevent the flatness of the lens array surface from being lowered due to scratches at the time of cutting, thereby improving the performance of an image device.

[0006]

The image device of the present invention is a combination of an image element and a lens array optically coupled to the image element, wherein at least a part of the lens surface of the lens array is made of a transparent synthetic resin. It is characterized by being coated.

[0007]

When the surface of the lens is coated with a transparent synthetic resin, the lens is shielded from ozone, nitrogen oxides, sulfur oxides, etc., and it is possible to prevent fogging of the lens.
As a result, the replacement life of the image device and the maintenance interval can be extended. This effect is particularly remarkable for glass lenses. The coated transparent synthetic resin can flatten the lens surface and eliminate the image disturbance due to the non-flatness of the surface, which is a problem particularly in the case of a plastic lens.

The coating with the transparent synthetic resin is not particularly limited, but can be used as follows. In both the case of a plastic lens and the case of a glass lens, the lens array has variations in the focal position. Such variations occur due to variations in the refractive index distribution within the lenses, variations in the length of individual lenses, different pitches between lenses, and lenses that are tilted and not aligned. It appears as a different variation for each lens. The variation in the focal position is larger than that in the case of a plastic lens and a glass lens. Regardless of whether the entire lens array varies equally from the standard, the variation in the focal position appears as the variation for each individual lens in one lens array. It is extremely difficult to correct such variations for each individual lens. Therefore, the dispersion of the focal position is corrected by utilizing the fact that the refractive index of the transparent synthetic resin coated is different from that of the surrounding air.

Assuming that the refractive index of the transparent synthetic resin is n, the surrounding medium is air and the refractive index is 1, when a transparent synthetic resin coating having a thickness of d is provided, the distance L between the lens and the light source surface or the image plane is L. Is
Equivalently shorten by ΔL = d · (n−1) / n (1). Therefore, if the image plane is too far from the lens, a transparent synthetic resin coating may be provided on the image plane side of the lens to apparently bring the image plane closer to bring the focus position to the image plane. On the other hand, when the light source surface is too far away, a transparent synthetic resin coating may be provided on the light source surface side of the lens to apparently bring the light source surface closer to each other so that the focal position can be adjusted. If the image plane is too close, a transparent synthetic resin coating is provided on the light source surface side of the lens. This is the spatial frequency M of the lens array.
The resolution expressed in TF does not decrease so much when the distance between the lens and the light source surface or the image forming surface is too long or both are too short, and significantly decreases when only one is too long or too short. This is what was used. Similarly, when the light source surface is too close, a transparent synthetic resin coating is provided on the imaging surface side of the lens. Since the transparent synthetic resin coating can be performed for each lens by measuring the variation of the focal position with a CCD element or the like, correction can be performed according to each individual lens. When correcting variations in the surface height of the LED array of the LED printer head, photoelectric element array, liquid crystal shutter array, etc., the variations in the focal position are measured and corrected with these elements integrated with the lens array. Then, the variation in the focal position of the lens array and the variation in the surface height of the LED array or the like can be simultaneously corrected.

[0010]

1 to 4 show the principle of correcting variations in the focal position of a lens. In each figure, the light source is on the left side of the figure, the image plane is on the right side of the figure, and light passes through the lens from left to right. The solid line shows the path of light before correction, and the broken line shows the path of light after correction with transparent synthetic resin. These displays are unified in all figures. 2 in each figure
Is a lens, which may be a separate glass lens or plastic lens of the self-focusing lens array. Reference numeral 4 denotes a transparent synthetic resin, preferably a transparent acrylic resin or a transparent silicon resin. In addition to this, a transparent epoxy resin or the like can be used as long as it is transparent and has high durability against acids such as nitric acid. 6 is a light source surface, and here, L of the LED printer head
Reference numeral 8 denotes an ED array, and 8 denotes an image plane, which is a photosensitive drum of a printer in this case.

FIG. 1 shows a state in which the light source surface 6 is too far away so that the focus position is farther than the image plane 8 (long focus).
FIG. 2 shows a state in which the focus position is ahead of the image plane 8 (short focus) because the position of the image plane 8 is too far away. The terms long focus and short focus are always used for the image plane 8 and not for the light source plane 6. Figure 3
Indicates that the image plane 8 is too close to have a long focus.
FIG. 4 shows a state in which the light source surface 6 is too close to have a short focus. In any of these states, the transparent synthetic resin 4 is coated on the light source surface 6 side if the focal length is long, and on the image forming surface 8 side if the focal length is short, to correct the focal position.

The principle of correction will be described. In the case of FIG. 1, if the transparent synthetic resin 4 is coated on the light source surface 6 side, the light source surface 6 apparently approaches according to the equation (1) when viewed from the lens 2. The apparent approach distance is ΔL, the distance between the lens 2 and the light source surface 6 or the image forming surface 8 is L, the thickness of the transparent synthetic resin 4 is d, the refractive index is n, and the surrounding medium is air and the refractive index is Is 1, ΔL = d · (n−1) / n (1). In the case of FIG. 2, the transparent synthetic resin 4 apparently brings the image plane 8 closer by .DELTA.L (removes the focus position by .DELTA.L) to correct the short focus state. In the case of FIG. 3, the image plane 8
Since the position is too close, it is in a long focus state, and the transparent synthetic resin 4 is coated on the light source surface 6 side. By doing so, the light source surface 6 apparently approaches the lens 2, and as a result, the long focus state can be corrected. This is because the resolution of the lens is less affected when the light source surface 6 and the imaging surface 8 are both too close or too far, and has a large effect when only one is too close or too far. It is a thing. That is, in the long focus state, the image forming surface 8 is too close, and the light source surface 6 is apparently brought closer. In the case of FIG. 4, since the light source surface 6 is too close, it is in a short focus state. Therefore, the transparent synthetic resin 4 is coated on the side of the image plane 8 so that the image plane 8 is apparently closer to correct the short focus state. As is clear from the above, if the transparent synthetic resin 4 is coated on the light source surface 6 side in the case of the long focus and on the image forming surface 8 side in the case of the short focus, the variation in the focus position can be corrected. ..

FIG. 5 shows a method of measuring the variation between the short focus and the long focus. Reference numeral 10 denotes a self-focusing lens array, in which an image sensor such as a CCD element or a photomultiplier tube is arranged at the position of the image forming surface 8 and the image forming state of the point light source from the light source surface 6 is observed. The light emitting diodes of the LED array are extremely small and can be said to be point light sources. In this state, the image sensor is moved to the left or right of the image plane 8 or in one direction of the left side or the right side, and the change in the beam diameter of the image beam is observed. In the case of short focus, when the position of the image sensor is changed from the image plane 8 to A and B as shown in FIG. 6, the beam diameter of the image beam at the position C becomes the minimum and increases again. On the other hand, in the case of long focus, the beam diameter of the image beam becomes the minimum at the position C, and the beam diameter increases as it moves to A and B.
Therefore, the position C where the beam diameter is the smallest is the short focus if it is in the front, and the long focus is if it is far. The image plane 8
The absolute value of the shift of the focal position is found from the shift distance of the position C from. When only moving the image sensor to the front side (to the A and B sides), from the change pattern of the beam diameter of the image beam at the image plane 8 and the positions A and B, and the relative value of the beam diameter at three points, The absolute value of the discrepancy between the short focus and the long focus and the deviation is found.

Specifically, the lens array 10 and the substrate of the LED array are set, and the image sensor is arranged at the position of the photosensitive drum. Then move the image sensor,
Whether there is a difference between the long focus and the short focus for each individual lens 2,
Measure the degree of deviation. After this, the lens array 10 is set to L
Separated from the substrate of the ED array, the short focal length lens 2 is coated with the transparent synthetic resin 4 on the image plane 8 side and the long focal length lens 2 is coated on the light source surface 6 side. The coating is performed for each lens 2,
The coating thickness is determined according to the value measured by the method of FIGS. After that, if the substrate on which the LED array is mounted and the lens array 10 are set, it is possible to simultaneously correct variations in height of individual light emitting diodes and variations in focal position for each lens 2. The focus position of the lens array 10 may be corrected by the lens array alone, and the height variation of the light emitting diodes may not be corrected. The transparent synthetic resin 4 applied in this manner also has a role of simultaneously protecting the surface of the lens 2 from nitric acid mist generated by the reaction between ozone and nitrogen in the air.

The variation of the focal position is large for the plastic lens and small for the glass lens. In a plastic lens, variation in the length of the lens 2 is large as a cause of variation in the focal position. Therefore, as shown in FIG. 8, the unevenness on the surface of the lens array 10 is measured to determine the coating position and the thickness of the transparent synthetic resin 4. When the image plane 8 side is concave like the lens 21, it has a short focal point, and the thickness of the transparent synthetic resin 4 is determined according to the degree of the concave, and the image plane 8 side is covered. When the light source surface 6 side is concave like the lens 22, it is a long focus and the light source surface 6 side is covered with the transparent synthetic resin 4. Lens 23
As described above, when the image forming surface 8 side is convex, it is a long focus and the light source surface 6 side is covered with the transparent synthetic resin 4. When the light source surface 6 side is convex like the lens 24, it has a short focus and the transparent synthetic resin 4 is coated on the image forming surface 8 side. When both are concave like the lens 25, both surfaces may be covered with the transparent synthetic resin 4 or may not be covered. When both lenses are convex like the lens 26, they are not covered, or the transparent synthetic resin 4 is coated on the side where the degree of convex is remarkable. The relationship between the unevenness on the surface of the lens 2 and the long focus or the short focus is clear from FIG.

FIG. 9 and FIG. 10 show modified examples in which both processes of flattening the plastic lens and correcting variations in focus accuracy are performed. In this case, as shown in FIG. 9, the entire surface of the lens array 10 is covered with a thin transparent synthetic resin 12 to flatten the surface. Then, as shown in FIG.
By determining the presence or absence and the degree of variation in the focal position of the short focus or the long focus, the correction by the transparent synthetic resin 4 is performed accordingly. The two transparent synthetic resins 12 and 4 may be applied at once.

For flattening the plastic lens, a pair of heaters 14 and 14 may be used as shown in FIG. 11 while heating both ends of the lens while applying pressure. For heating, in addition to direct heat conduction from the heater 14, any heating such as infrared heating or microwave heating may be used. FIG. 12 shows the lens array 10 after flattening. If the focal position shift correction is performed on the flattened lens array 10 by the method shown in FIGS. 5 and 8, the lens array subjected to both the flattening process and the focus position shift correction as in FIG. Is obtained. If the pressure and the heating temperature are increased in the flattening of FIG. 11, not only the surface of the lens 2 is flattened, but also the unevenness shown in FIG. 8 is eliminated and the variation in the focal position can be corrected.

FIG. 13 shows a modification suitable for a glass lens, in which the lens surface is protected and the focal position is varied. In this case, the presence / absence and the degree of variation in the focal positions of the short focus and the long focus are measured for each lens 2 by the method shown in FIGS. Then, based on this, the coating amount of the transparent synthetic resin 4 is determined, and the both sides are coated with the transparent synthetic resin 4. The thickness of the transparent synthetic resin 4 is minimized in the lens 27 where the focal position does not vary, and in the case of the lens 28 where the focal position varies, the transparent synthetic resin 4 on the image plane 8 side is thick in the case of short focus.
In the case of a long focus, the transparent synthetic resin 4 on the light source surface 6 side is thickly applied and correction is performed.

[0019]

According to the present invention, it is possible to prevent the fogging of the lens array due to ozone or the like and to prevent the flatness of the surface of the lens array from being deteriorated due to scratches at the time of cutting, thereby improving the performance of the image device.

[Brief description of drawings]

FIG. 1 is a diagram showing correction in a case where a distance between a light source surface and a lens is too long in an embodiment.

FIG. 2 is a diagram showing correction when the distance between the image forming surface and the lens is too long in the example.

FIG. 3 is a diagram showing correction when the distance between the image forming surface and the lens in the embodiment is too short.

FIG. 4 is a diagram showing correction when the distance between the image forming surface and the lens is too short in the example.

FIG. 5 is a diagram showing correction of variations in focal position of the lens array in the example.

FIG. 6 is a diagram showing measurement of focal position variation in the example.

FIG. 7 is a diagram showing measurement of focal position variation in the example.

FIG. 8 is a diagram showing correction of focus position variation in a modified example.

FIG. 9 is a diagram showing flattening of a lens surface by coating with a transparent synthetic resin in an example.

FIG. 10 is a diagram showing correction of focal position variation after the lens surface is flattened in the example.

FIG. 11 is a diagram showing flattening of a lens surface in another modification.

FIG. 12 is a diagram showing a lens surface after flattening in a modification of FIG.

13 is a diagram showing correction of focal position variation after flattening of the lens surface in the modification of FIG.

[Explanation of symbols]

 2 lens 4 transparent synthetic resin 6 light source surface 8 image forming surface 10 lens array 12 transparent synthetic resin 14 heater

Claims (1)

Claim: What is claimed is: 1. An imaging device comprising an image element and a lens array optically coupled to the image element, wherein at least a part of the lens surface of the lens array is made of a transparent synthetic resin. An imaging device characterized by being coated.